1. Field of the Invention
This invention relates to a bearing blanket for an extended nip press. More particularly, this invention relates to a bearing blanket for an extended nip press in which the blanket, a felt and a formed web pass through an extended nip defined by a rotatable press roll and a cooperating hydraulically loaded shoe.
2. Information Disclosure Statement
Traditionally, a press section of a papermaking machine has included a pair of counter rotating press rolls defining therebetween a nip for the passage therethrough of a formed web disposed adjacent a felt or between a pair of felts. With such prior art press nips not only is the residence time of the web within the nip very short, but the pressure applied to the formed web is extremely high.
With the advent of the extended nip press, the residence time of the web within the nip is greatly increased and the pressure exerted on the moving web can be significantly reduced. Not only does the extended nip press produce a pressed web which is 5 to 10 percentage points dryer than the corresponding web produced on conventional presses, but such extended nip presses result in the individual fibers within the formed web being pressed closer together thereby resulting in an improved quality in the end product.
The extended nip press includes a bearing blanket, a felt and a formed web which pass through an extended nip defined by a rotatable press roll and a cooperating hydraulically loaded shoe. The hydraulically loaded shoe urges the blanket against the felt during passage through the extended nip such that water is squeezed from the felt and web thus imparting an improved dewatering action.
The pressed web produced by such an extended nip press results in a paper web having 20 percent less water per ton compared with a similar web produced on a conventional press section. Therefore, the energy expended in the dryer section of the papermaking machine is correspondingly reduced. Additionally, production is increased by 25 percent. Furthermore, because of the increased residence time of the formed web in the extended nip, more water is able to migrate from the formed web into the felt.
In practical terms, for every gallon (3.8 liters) of water removed from a moving web in a conventional press section an extra 0.95 liters of water are removed with the extended nip press.
However, in earlier non vented extended nip presses bearing blankets of non vented construction having a continuous looped configuration were utilized. In such solid type blankets, water exuding from the felt during passage of the felt and blanket through the extended nip was unable to flow sufficiently quickly from the extended nip in order to avoid being entrapped between the felt and adjacent blanket during the passage of the web through the extended nip. Water so entrapped not only increased the fluid pressure within the extended nip, but also tended to rewet the formed web.
In an attempt to overcome the aforementioned problem, grooved blankets have been proposed in which a plurality of parallel grooves are formed parallel to the machine direction of the blanket so that water exuding from the felt by the interaction of the felt and blanket is able to flow unimpeded through the multiplicity of grooved channels and thereby inhibit the detrimental buildup of water pressure within the extended nip.
These grooved blankets or blankets having a plurality of recesses for the reception therein of water flowing from the felt have proved only partially successful because although such grooved blankets operate very successfully initially, there exists a tendency for such grooves to be crushed after extended use of the blanket.
The present invention provides a bearing blanket including a woven base and a first and second laminate. The second laminate defines a plurality of parallel grooves and is of urethane having sufficient hardness to inhibit crushing of the grooves while the first laminate is of a lesser hardness for permitting flexing of the second laminate during passage through the extended nip.
In the prior art, a number of patents teach bearing blankets having a plurality of recesses.
U.S. Pat. No. 4,482,430 to Tampella AB describes particularly with reference to FIG. 6 and column 4, lines 27-33, a band 2 having a grooved or blind bored surface layer disposed adjacent to the felt. According to column 4, line 23, the band is fabricated from urethane reinforced with a nylon fabric with water used as the lubricant for the extended nip press. Column 4, lines 20 and 21 describe the urethane elastic material as having a high restoring capability. Column 4, line 30 describes the hardness of the opposite surfaces of the band as being different from each other. No direct reference is made to the need for a particular hardness of the urethane band. However, a surface of the band is claimed and this surface faces the sliding surface of the loading shoe and is provided with "separated recesses for receiving the lubricating medium, said recesses being entirely closed by the sliding surface of said loading shoe when said recesses are within said press zone." Other claims recite various features of the recesses including cup-shaped, rectangular, longitudinal, transverse and oblique grooves or recesses.
U.S. Pat. No. 4,287,021 to Justus teaches an extended nip press and claim 9 discloses a means defining grooves on the inside of the belt with the grooves spiraling towards the center of the belt to move lubricant inwardly along the belt. Additionally, column 3, lines 19-24 define the outer surface of the roll 10 as having grooves therein to aid in the reception of water by the felt 23. More particularly, the outer surface of the belt 25 is similarly grooved to aid in the passage of water from the web into the felt 24. Column 2, lines 23-24 describe the belt as being formed of heavy rubber or reinforced rubber.
Column 2, lines 64-69 describe the belt as being provided with grooves formed on the inner surface thereof as shown by the grooves 42 in the surface 43 of the belt in FIG. 3. This specification states that this tends to work the lubricant towards the center of the belt, with the grooves being relatively shallow so as not to weaken the belt and are preferably disposed in the spiral pattern with the spiral extending towards the center relative to the direction of travel of the inner surface of the belt.
Although such spiral configuration is described as stated hereinbefore, such spiral configuration is not clearly shown in FIG. 3 or any other figures of drawings.
U.S. Pat. No. 4,431,045 to Josephson describes with reference column 3, lines 50-58 a belt for an extended nip press having sufficient hardness to take up and distribute load without excessive deformation while being sufficiently flexible. Polyurethane of durometer hardness in the range of 80 to 85 and approximately 1/4" (0.64 cms) in thickness is stated to be useful for some purposes.
Column 2, lines 52-55 teach that the belts may have recesses on the outer side which face the surface of the roll for draining liquid from the pressed web. Alternatively, the belt may have a plurality of apertures for drainage. Furthermore, belt 10 is suitably made of rubber or a flexible plastic. Polyurethane is used in the embodiments of FIGS. 2 and 3.
Column 2, lines 20-28 teach that in the embodiment of FIGS. 2 and 3 a plurality of continuous parallel grooves 92 extend longitudinally on the outer side of the belt for drainage. Alternatively, FIG. 8 illustrates a belt 10.2 having a plurality of apertures 90 or 96 for drainage. As shown in FIG. 9, apertures 94 extend completely through the belt. Alternatively, as seen in FIG. 10, blind-drilled apertures 96 may be used.
U.S. Pat. No. 4,492,611 to Meinandor teaches in Column 2, line 16, an endless water impervious belt 4 and 5 for use in conjunction with an extended nip press.
U.S. Pat. No. 4,496,429 to Salminen assigned to Tampella teaches an endless band running around two band rolls of an extended nip press. Column 2, lines 51-53 teach drillings 10 as shown in FIG. 5 or holes or grooves for receiving water from the felt in the press surface of the V-bands or V-belts.
U.S. Pat. No. 4,503,765 to Voith discloses at Column 3, lines 34-40 a pressure belt 21 as being impermeable to liquid and is "lubricated with oil on its inner surface by means of devices not illustrated."
U.S. Pat. No. 4,425,190 to Cronin describes an extended nip press including a belt generally designated "compliant transport systems." This specification does not include details as to whether the belt is grooved in any way and the main thrust of the specification resides in the concept of introducing the belt 32 over lubricant reservoir 40 prior to coming into contact with the lower felt 30 and subsequent passage through the extended nip.
U.S. Pat. No. 4,427,492 to Cronin discloses an extended nip press having a compliant belt 32. This specification makes no mention of such belt 32 as being grooved and no reference is made to the belt being fabricated from urethane. Column 4, lines 61-69 teach the compliant belt 32 as being 0.3" (0.76 cm) thick in the non-compressed state with belt 32 compressing to 0.29" (0.74 cm).
Column 5, lines 25-30 teaches that belt 32 distorts sideways during movement along the nip shoe compliant belt interface and that this sideways distortion brings the compliant belt 32 to the side edges 58 of the nip shoe 24.
U.S. Pat. No. 4,428,797 to Cronin teaches at column 4, line 63 the belt 32 as being compressed to 0.29" (0.74 cm).
U.S. Pat. No. 3,775,243 to McCarrick teaches at column 2, lines 12-13 a granite press roll 13 having a grooved surface 16 as shown in FIG. 2.
U.S. Pat. No. 4,459,907 to Sundman teaches a belt for moving water from a moving layer of peat. The belt includes a plurality of recesses or compression chambers 9 of truncated pyramid configuration as shown in FIG. 2.
U.S. Pat. No. 4,353,296 to Beucker discloses a rubber covered nip roll in which an elastomer cover is grooved circumferentially and in which the modulus of elasticity of the cover is greater in a transverse direction than in the circumferential direction in order to prevent or reduce closing up of the grooves during passage through the nip area.
U.S. Pat. No. 4,330,023 to Cronin teaches a belt 216 of an extended nip press in which lateral edges of the belt are disposed outside the pressure shoe area.
British Patent No. 2,106,555A to Albany International Corporation describes a belt of an extended nip press in which the belt includes a base fabric 20, as shown in FIG. 3. The fabric 20 is impregnated with polyurethane 22. The specification does not disclose a grooved belt or the hardness of the polyurethane coating.
British Patent No. 2,106,557A to Albany International Corporation teaches a belt 16 for an extended nip press and lines 124-129 teach that the belt 16 comprises a two layer woven monofilament base fabric 20 which has multifilament or spun stuffer yarns 21 impregnated on one face with a polymeric material 22 such as polyurethane. This specification does not disclose a grooved belt or differential hardness of polyurethane.
EPO Patent No. 138,797 to Yamauchi Rubber Industries, Ltd. teaches an endless belt for an extended nip press in which the yarns in the direction transversely across the belt running direction do not need a high strength. This specification makes reference to the two aforementioned British Albany patents. No reference is made to grooved belts or the hardness of the polyurethane coating.
U.S. Pat. No. 4,364,421 to Martin describes a dryer fabric of woven construction including means for joining the respective ends of the felt together to form a continuous loop.
U.S. Pat. No. 4,221,373 to Muller is marginally relevant in that the specification describes an endless belt 13 shown in FIG. 3 as being provided with a V-shaped groove 17 along the length thereof.
British Patent No. 2,142,946A in the name of Osakeyhito describes an extended nip press including a loaded, stiff, endless flexible belt.
British Patent No. 2,127,449A to Bergstrom teaches on page 2, lines 66-68 a traveling belt 25 which is of strong material, such as reinforced rubber used in extended nip presses. No disclosure is made of the grooved belt and no details as to hardness are taught in the specification.
Canadian No. 1,068,525 to Schmitt and Rempel is marginally relevant in disclosing a belt 16a and 21a for an extended nip press as shown in FIG. 1. Another embodiment shown in FIG. 2 teaches a belt 116a and 121a, respectively. No details as to construction of such belts is made or any reference to such belts being grooved.
French No. 2,153,218 to Scaal teaches on page 2, lines 7-12 a belt 2a of urethane material.
U.S. Pat. No. 4,483,745 to Wicks et al teaches an extended nip press having an endless traveling impervious belt 15, the hardness of which is in the range 10 to 200 P and J. This specification does not disclose such belt 15, 40 or 60 according to the various embodiments of the invention as being grooved.
U.S. Pat. No. 4,353,828 to Weyerhaeuser teaches a dryer for a papermaking machine including a fabric and cylinder combination Column 4, lines 13-16 teach that the fabric may include circumferential grooves.
U.S. Pat. No. 4,359,827 to Weyerhaeuser discloses in Column 13, lines 60-67 that the dryer fabric may alternatively include circumferential grooves and the fabric must be permeable in order for the vacuum to communicate through the fabric and hold the web or sheet to it.
EPO No. 117,212 to Allan Angogna shows with reference to FIG. 5, a roll having grooves 22, 23 and 24 described on pages 8, lines 25-27.
EPO No. 107,607 to Justus teaches an extended nip press having a belt B. However, no details are given as to the composition of the belt or hardness thereof. No disclosure is made as to whether the belt is grooved or not.
EPO No. 109,220 to Arav relates to a hydraulic control system for an extended nip press. No details are given as to the blanket or whether the blanket is grooved or not.
EPO No. 64,933 to Justus discloses an extended nip press having impervious belts 16 and 17 sandwiching the felt and web therebetween. The belts are not disclosed as being grooved, but the traction rolls 20 and 22 are grooved.
None of the aforementioned prior art disclose a blanket having a first and second laminate having differential hardness relative to each other for inhibiting crushing of the venting or drainage grooves. Therefore, it is a primary objective of the present invention to provide a bearing blanket for an extended nip press having improvements which overcome the inadequacies of the prior art proposals and which provides a significant contribution to the papermaking art.
Another objective of the present invention is the provision of a bearing blanket for an extended nip press in which the blanket includes a first laminate which cooperates with the shoe, and a second laminate defining a plurality of grooves, the first and second laminates having a hardness differential relative to each other which permits flexing of the first laminate and inhibits crushing of the grooves during passage of the blanket through the extended nip.
Another object of the present invention is the provision of a bearing blanket in which the first laminate has a hardness within the range 80 to 93 Shore "A", thereby permitting the laminate to flex during passage through the extended nip.
Another object of the present invention is the provision of a bearing blanket in which the second laminate has a hardness of at least 94 Shore "A", thereby inhibiting crushing of the plurality of recesses during passage of the blanket through the extended nip so that fluid flow from the felt is unimpeded.
Another object of the present invention is the provision of a bearing blanket in which the second laminate has a thickness which is greater than the thickness of the first laminate, thereby having sufficient thickness to accommodate a plurality of parallel grooved recesses therein.
Another object of the present invention is the provision of a bearing blanket in which the second laminate has a hardness of at least 99 Shore "A" to inhibit crushing of the plurality of grooves.
Other objects of the present invention will be apparent to those skilled in the art and from the detailed description taken in conjunction with the accompanying drawings, and it will be appreciated by those skilled in the art that the present invention is equally applicable to extended nip presses utilizing two felts and using any combination of plain, vented or grooved rolls.